A cooling device for a vehicle is known that is provided with a cooling water circuit for circulating cooling water through the inside of an engine by driving a pump and a thermostat in a part of the cooling water circuit that is downstream of the engine. The thermostat permits and inhibits passage of the cooling water through the inside of the engine by selectively opening and closing a valve body in accordance with the temperature of the cooling water.
A thermostat having such a configuration inhibits the passage of the cooling water by closing the valve body if the temperature of the cooling water is low. On the other hand, if the temperature of the cooling water is high, the thermostat opens the valve body by using a thermoelement that receives heat from the cooling water, thereby permitting the passage of the cooling water inside of the engine. By selectively opening and closing the valve body of the thermostat in such a manner, the passage of the cooling water through the inside of the engine is inhibited if the engine is cold owing to the low cooling water temperature, thereby promoting warming up of the engine. On the other hand, if the temperature of the cooling water is high, the passage of the cooling water through the inside of the engine is permitted, to prevent the cooling water inside the engine from boiling.
It is to be noted that immediately after the engine starts from the cold state, the cooling water in the cooling water circuit is low in temperature, so that the thermostat is closed to promote warming up of the engine. In such a case, the thermostat is closed to inhibit the passage of the cooling water through the inside of the engine. In this state, if heat is generated a lot in a combustion chamber owing to a high-load operation of the engine, such a situation occurs in which the temperature of the cooling water only in the cylinder head of the engine rises while the temperature of the cooling water around the thermostat element does not rise. In such a situation, the cooling water stagnant in the cylinder head of the engine receives heat from the combustion chamber so that its temperature may rise excessively, and can start boiling.
To cope with such a situation, a device described in Patent Document 1 is provided with a heat generator in a thermostat for heating a thermoelement. By permitting the heat generator to heat the thermoelement, a valve body can be opened even if cooling water around the thermoelement is low in temperature. In this case, if the cooling water in the cylinder head of the engine in a condition where the thermostat valve body is closed reaches a temperature at which the water will possibly boil, the thermoelement is heated by the heat generator of the thermostat, thereby opening the valve body. By permitting the passage of the cooling water to the inside of the engine by opening the valve body in such a manner, it is possible to prevent the water stagnant in the cylinder head from boiling.